The present invention relates to a color cathode ray tube which is equipped with an electromagnetic field leakage preventing coating, and, more particularly, to a color cathode ray tube having a field leakage preventing coating in the form of a double coating film composed of a conductive high-refractive first layer and a low-refractive second layer adhering on the surface of a faceplate of a panel section of the cathode ray tube envelope.
There is a conventional cathode ray tube in which a double coating film, composed a high-refractive first layer and a low-refractive second layer, is adhered on the outer surface of a faceplate of a panel section of the tube envelope to prevent glare on the faceplate, to prevent the accumulation of an electric charge which may produce an electrical shock when touching the faceplate and to provide an improved contrast in a displayed image produced by the cathode ray tube.
Here, the anti-reflection function of the cathode ray tube having the conventional double coating film is achieved by interference of light caused by the double coating film.
The electrical charge preventing function for preventing an electrical shock when touching the cathode ray tube having the conventional double coating film is achieved by reducing the surface sheet resistance (hereinafter abbreviated as a surface resistance) of the conductive high-refractive first layer to 104 to 108 xcexa9/xe2x96xa1 by using a conductive high-refractive first layer, into which conductive particles, including tin oxide (SnO2) and antimony oxide (Sb2O3), are combined, or into which conductive particles, including tin oxide (SnO2) and indium oxide (In2O3), are combined, for example.
Further, the function for providing a high contrast in the image displayed by the cathode ray tube having the conventional double coating film is achieved by mixing a certain amount of pigment of a specific color into the high-refractive first layer of the double coating film.
As the surface treatment film formed on the outer face of the faceplate of the panel section of such a color cathode ray tube, there have been known 1) one which is obtained by forming a conductive film having a resistance of about 1xc3x97103 xcexa9/xe2x96xa1 by means of sputtering, evaporation or the like to prevent electrical charge accumulation and to suppress leakage of electromagnetic waves, and by forming thereon a multi-layered film in which a low-refractive film and a high-refractive film are laminated, 2) one which is obtained by forming a NESA coating film on the outer face of the panel by means of CVD or the like as a conductive film and by laminating thereon a high-refractive film, or 3) one which is obtained by forming a conductive film by applying a solution in which particles of silver (Ag), whose specific resistance is low, are dispersed by application means, such as spin coating, and by forming thereon a low-refractive layer made of silica (SiO2) by means of spin coating or the like.
It is noted that the technological features for achieving the above-mentioned functions have been disclosed in Japanese Patent Laid-Open Nos. Hei. 3-93136, Hei. 5-113505, Hei. 5-343008 and Hei. 7-312170.
In addition, there also is a known cathode ray tube which prevents an electric field generated within the cathode ray tube from leaking from the outer face of the faceplate of the panel section, i.e. a cathode ray tube having a field leakage preventing coating film, provided by adhering and forming a double coating film composed of a high-refractive first layer and a low-refractive second layer on the outer face of the faceplate of the panel section of the tube envelope and by using a conductive high-refractive first layer, in which metal particles are mixed, as the high-refractive first layer to reduce the surface resistance of the conductive high-refractive first layer to less than 1xc3x97103 xcexa9/xe2x96xa1, and an example thereof is described in a magazine xe2x80x9cIndustrial Materialxe2x80x9d vol. 44, No. 9 (August, 1996) pp. 68-71.
By the way, the above-mentioned cathode ray tube having the double coating film has had a problem in that, although a conductive high-refractive first layer into which conductive particles, such as tin oxide (SnO2) and antimony oxide (Sb2O3), are combined, or conductive particles, such as tin oxide (SnO2) and indium oxide (In2O3), are combined, for example, is used, it has not been possible to prevent the electric field generated within the cathode ray tube from leaking to the outside through the outer face of the faceplate of the panel section on which the conductive high-refractive first layer is provided because the surface sheet resistance of the conductive high-refractive first layer is 1xc3x97104 to 108 xcexa9/xe2x96xa1.
The prior art cathode ray tube having the field leakage preventing coating film using particles of silver (Ag) also has had a problem in that the film does not provide enough mechanical strength.
The prior art cathode ray tube having a field leakage preventing coating film has had another problem in that, although it allows a high contrast to be obtained by suppressing the black color of the body of the cathode ray tube, which is caused by the double coating film composed of a conductive high-refractive first layer and a low-refractive second layer, along with an increase of reflection of external light on the fluorescent screen within the faceplate from standing out due to the light absorptivity of the metal particles mixed into the conductive high-refractive first layer, the body color of the cathode ray tube is colored to a color other than black because the spectral transmittance of the mixed metal particle layer differs depending on the wavelength of the light. For instance, when the spectral transmittance of the layer of the mixed metal particles is low, such as around 420 nm in wavelength, and shows a peak of absorption, the double coating film composed of a high-refractive first layer and a low-refractive second layer turns out to have an amber color, a hue inadequate for the display.
The prior art color cathode ray tube having the structure 1) described above has had a problem in that, although it effectively prevents glare and the accumulation of an electric charge and suppresses the leakage of electromagnetic waves, its production cost is remarkably high. The color cathode ray tube having the structure 2) described above has had a problem in that it requires a number of steps for forming the NESA coat and the multi-layered film and that a desired performance cannot be fully obtained. The color cathode ray tube having the structure 3) described above has had a problem in that it is difficult to maintain the initial performance for a long period of time, though its production cost is low.
Accordingly, it is a primary object of the present invention to provide a cathode ray tube equipped with a field leakage preventing coating film which makes it possible to prevent aged deterioration of a surface sheet resistance of a conductive high-refractive first layer within a double coating film composed of a conductive high-refractive first layer and a low-refractive second layer.
It is a secondary object of the present invention to provide a cathode ray tube equipped with a field leakage preventing coating film which makes it possible to prevent the aged deterioration of the surface sheet resistance of the conductive high-refractive first layer within the double coating film, composed of a conductive high-refractive first layer and a low-refractive second layer, and to prevent the body of the cathode ray tube from being colored.
In order to achieve the first object, the inventive cathode ray tube having the field leakage preventing coating film is provided with first means in which a conductive high-refractive first layer is formed by mixing particles of one or more metals among the noble metal elements of gold (Au), silver (Ag) and platinum (Pt) to form a double coating film composed of a conductive high-refractive first layer mainly composed of the metal particles and a low-refractive second layer.
According to the first means, because the particles of one or more metals among the noble metal elements of gold (Au), silver (Ag) and platinum (Pt), which are chemically stable, are used as the metal particles of the conductive high-refractive first layer, the surface sheet resistance of the conductive high-refractive first layer may be reduced to 1xc3x97103 xcexa9/xe2x96xa1 which exerts a field leakage preventing function, and, at the same time, no age deterioration of the surface sheet resistance of the conductive high-refractive first layer is caused.
Further, in order to achieve the second object, an inventive cathode ray tube having a field leakage preventing coating film is provided with second means by forming a double coating film composed of a conductive high-refractive first layer in which metal particles are mixed and a low-refractive second layer, on the outer face of the faceplate of the panel section, by forming the conductive high-refractive first layer by mixing particles of one or more metals among noble metal elements of gold (Au), silver (Ag) and platinum (Pt) and by adding a coloring matter, such as a pigment or dye, to the low-refractive second layer to exert a wavelength selective absorbing characteristic.
According to the second means, beside the fact that the conductive high-refractive first layer has a low resistance of less than 1xc3x97103 xcexa9/xe2x96xa1 which produces a field leakage preventing function and that no age deterioration of the surface sheet resistance occurs similar to the first means described above, the body color of the cathode ray tube may be changed to an achromatic color by adding coloring matter which is complementary to the coloring of the body color of the cathode ray tube to the low-refractive second layer.
The color cathode ray tube of the present invention is characterized in that, in contrast to the prior art, it is provided with a low resistant conductive film formed by using a solution in which particles of chemically stable noble metals other than silver, or a noble metal mixed dispersed solution in which the ratio of silver is reduced, on the outer face of the faceplate.
The noble metals, other than silver, have a higher specific resistance than silver. Therefore, in order to obtain a desirable surface resistance, according to the present invention, the film is thickened to reduce the surface resistance and the drop of light transmittance in the visual range caused by the light absorbing characteristic intrinsic to the metal material due to the increase in the thickness is solved by using a faceplate having a high transmittance.
That is, a color cathode ray tube according to a first aspect of the invention comprises a vacuum envelope, comprising a panel section in which a fluorescent film made of at least one color of fluorescent substance is formed on the inner face thereof, a neck section in which an electron gun is mounted and a funnel section connecting the panel section and the neck section. The color cathode ray tube also has a multi-layered surface treatment film composed of a conductive high-refractive film formed on the outer face of the panel section and a low-refractive film formed thereon. The average light transmittance of the visual range in the surface treatment film is 50 to 70% and the surface resistance thereof is less than 1xc3x97103 xcexa9/xe2x96xa1. By employing the construction as described above, the leakage of electromagnetic waves may be fully suppressed and the anti-reflection and electric charge preventing functions may be fully achieved.
A color cathode ray tube according to a second aspect of the invention is characterized in that the conductive high-refractive film in the cathode ray tube of the first aspect of the invention contains a mixture of particles of one or more noble metals, except for silver, or a mixture in which silver particles are mixed in with particles of another noble metal.
Because the electrical resistance of the conductive film may be lowered by employing the construction as described above, the leakage of electromagnetic waves may be fully suppressed and the anti-reflection and electric charge preventing functions may be fully achieved.
Further, according to a third aspect of the invention, the particles of noble metal in the color cathode ray tube in the second aspect of the invention are one of platinum, rhodium, ruthenium, palladium, iridium and osmium.
Because the electrical resistance of the conductive film may be lowered by employing the construction as described above, the leakage of electromagnetic waves may be fully suppressed and the anti-reflection and electric charge preventing functions may be fully achieved.
According to a fourth aspect of the invention, the low-refractive film in the color cathode ray tube in the first, second or third aspects of the invention has a light scattering characteristic.
Because the resistance of the conductive film may be lowered by employing the construction as described above, the leakage of electromagnetic waves may be fully suppressed, readily satisfying the international guideline of TCO, and the anti-reflection and electric charge preventing functions may be fully achieved.
Further, because the specific resistance of the above-mentioned noble metals, other than silver, is large, the thickness may be increased in order to provide a conductive film having a desired resistance. The transmittance of the conductive film decreases by thickening the film. Then, the overall transmittance is set at a desired value by using a panel whose transmittance is large, or more concretely, a panel using a glass ground whose absorption coefficient is 0.001 to 0.03 mmxe2x88x921 as provided in the cathode ray tube of a fifth aspect of the invention.
The transmittance of the faceplate may be arbitrarily set and a panel having a desired contrast may be constructed by selecting the thickness of the above-mentioned conductive film or the absorption coefficient of the panel glass. Further, the external reflection curve may be flattened by thickening the conductive film, and the coloring caused by the transmittance, which differs depending on wavelength of light and the reflection of the body color of the fluorescent substance, may be reduced, allowing a high image quality color cathode ray tube to be obtained.
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which like numerals refer to like parts.